Silicon-based functional matrix substrate and optical integrated oxide device

ABSTRACT

An optical integrated oxide device uses a silicon-based functional matrix substrate on which both an oxide device and a semiconductor light emitting device can be commonly integrated with an optimum structure and a high density. A single-crystal Si substrate has formed on its surface a first region where a cleaned surface of the single-crystal Si substrate itself appears, and a second region in which a CeO 2  thin film is preferentially (100)-oriented or epitaxially grown on the single-crystal Si substrate. A semiconductor laser is integrated in the first region by epitaxial growth or atomic layer bonding, and an optical modulation device or optical detection device made of oxides are formed in the second region, to make up an optical integrated oxide device. A MgAl 2  O 4  thin film may be used instead of CeO 2  thin film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a silicon-based functional matrix substrateand an optical integrated oxide device, especially suitable for use inoptical integrated oxide electronics spread out on silicon.

2. Description of the Related Art

It is a well-known fact that oxide thin film materials have beenremarkably developed in recent several years, starting fromhigh-temperature superconductive oxides reported in 1986 ((1) Z. Phys.B., 64, 189-193(1986), (2) MRS Bulletin, XVII, No. 8, 16-54(1992), (3)MRS Bulletin, XIX, No. 9, 21-55(1994)).

On the other hand, memory devices using ferroelectric materials, whichwere energetically studied in a certain period of 1950s ((4) ElectricalEngineering, 71, 916-922(1952), (5) Bell Labs. Record, 33,335-342(1955)) but failed to penetrate into industries because ofdifficulties in, for example, controlling interfaces, have recently cometo be highlighted, and researches and developments thereon haveprogressed rapidly. The current aspect of the ferroelectric nonvolatilememory devices were reported in detail (for example, (6) Appl. Phys.Lett., 48, 1439-1440(1986), (7) U.S. Pat. No. 4,713,157, (8) IEDM Tech.Dig., 850-851(1987), (9) IEEE J. Solid State Circuits, 23,1171-1175(1988), (10) Tech. Dig. ISSCC 88, 130-131(1988), (11) AppliedPhysics, Vol. 62, No. 12, 1212-1215(1993), (12) Electronic Ceramics,Vol. 24, Jul., 6-10(1993), (13) Electronic Materials, Vol. 33, No.8(1994) (Special Vol. entitled "Application of Ferroelectric Thin Filmsto Nonvolatile Memory"), (14) Ceramics, Vol. 27, 720-727(1992)).

It is needless to say so on oxide superconductive devices (seeLiteratures (2) and (3)), it is well known also that researches anddevelopments have been proceeded recently on applications of oxidenonlinear optical devices and elements, as well. While fields ofsuperconductive devices and ferroelectric nonvolatile memory devices areunder remarkable development, in the field of optical devices,conciliation with lithographic techniques favorably used for silicondevices has not been prosecuted, as shown by the fact that bulkmaterials are still used, for example.

The Inventor, however, has recognized formerly that the importance ofepitaxial thin films of oxides on silicon is not limited only tosuperconductive devices or ferroelectric nonvolatile memory device, andmade some reports or proposals on oxide stacked structures made bystacking oxide thin films on silicon substrates and ferroelectricnonvolatile memory devices using them ((15) Japanese Patent Laid-OpenNo. Hei 8-330540, (16) Japanese Patent Laid-Open No. Hei 8-335672, (17)Japanese Patent Laid-Open No. Hei 8-340087, (18) Japanese PatentApplication No. Hei 8-336158, (19) J. Ceram. Soc. Japan. Int. Edition,103, 1088-1099(1995), (20) Mater. Sci. Eng. B., 41, 166-173(1966).

On the other hand, in optical integrated oxide electronics, it isrequired to integrate a semiconductor laser or other semiconductor lightemitting device together with an oxide optical device or other oxidedevice on a common substrate. However, as far as the Inventor is aware,there has been almost no substantial report on concrete devicestructures. Especially on optical integrated oxide devices in whichoxide elements are formed by epitaxial growth of oxides, no report hasbeen heard of.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a silicon-basedfunctional matrix substrate for integrating thereon an oxide device,such as oxide optical device, ferroelectric nonvolatile memory and oxidesuperconductive device, and a semiconductor light emitting device, suchas semiconductor laser, in an optimum structure with a high density.Another object of the invention is to provide an optical integratedoxide device using the silicon-based functional matrix substrate.

To attain the object, the Inventor made specific researches on optimumstructures, materials, processes, and so forth, for integrating an oxidedevice, such as oxide optical device, ferroelectric nonvolatile memoryand oxide superconductive device, and a semiconductor light emittingdevice, such as semiconductor laser, on a common substrate. Theseresearches are summarized below.

Selected as the substrate is a single-crystal silicon substrate which isa proven basic material of semiconductor memory, inexpensive, easilyavailable and excellent in crystallographic property.

To make an oxide device on a single-crystal silicon substrate, it wouldbe advantageous to epitaxially grow an oxide thin film on thesingle-crystal silicon substrate. Usually, however, it is difficult toepitaxially grow an oxide thin film directly on a single-crystal siliconsubstrate. It is therefore considered that a buffer layer of a materialin lattice match with a single-crystal silicon substrate be first grownepitaxially or oriented preferentially on the single-crystal siliconsubstrate, and an oxide thin film in lattice match with the buffer layerbe thereafter grown epitaxially on the buffer layer. In this manner, amaterial most suitable for the oxide device to be made can be selectedfrom a wide variety of oxides. The buffer layer is preferably made of anoxide to ensure epitaxial growth of an oxide thin film thereon. Thebuffer layer made of an oxide is preferably epitaxially grown directlyon the single-crystal silicon substrate.

Oxide materials that can be epitaxially grown directly on asingle-crystal silicon substrate are currently only five, namely,magnesium oxide (MgO), cerium oxide (ceria) (CeO₂), α alumina (α-Al₂O₃), yttrium stabilized zirconium (YSZ) and magnesium aluminum spinel(MgAl₂ O₄), as shown in Table 1. This does not mean that the otheroxides have been proved not to epitaxially grow directly onsingle-crystal silicon substrates, and there might be one or more, otherthan the above five oxides, which can be epitaxially grown directly.Table 1 shows lattice constants (a, c) of oxide crystals and thermalexpansion coefficients (α) (some of the data relies on "Structure andProperties of Inorganic Solids" by F. S. Galasso (Int. Series ofMonographs in Solid State Physics, Vol. 7). The lattice constant andthermal expansion coefficient of silicon (Si) are a=0.5430884 nm andα=3.0×10⁻⁶ /K, respectively.

                  TABLE 1                                                         ______________________________________                                        Oxide  Type of Crystal                                                                             Lattice Constant                                         Crystal                                                                              Structure     (nm)           α[10.sup.-6 /K]                     ______________________________________                                        MgO    halite: NaCl  a = 0.4213     13.6                                      CeO.sub.2                                                                            fluorite: CaF.sub.2                                                                         a = 0.5411     8.9                                       α-Al.sub.2 O.sub.3                                                             corundum: α-Al.sub.2 O.sub.3                                                          a = 0.476 c = 1.299                                                                          8.3                                       YSZ    halite: CaF.sub.2                                                                           a = 0.514 (a.sub.p = 3.63)                                                                   7.6 (ZrO.sub.2)                           MgAl.sub.2 O.sub.4                                                                   spinel: MgAl.sub.2 O.sub.4                                                                  a = 0.8083     7.18                                      ______________________________________                                    

Among these oxide materials, MgO, CeO₂, α-Al₂ O₃, YSZ and MgAl₂ O₄, CeO₂and MgAl₂ O₄ are most prospective because they are less subject toproblems by diffusion of their component elements, and promise a higherpossibility of epitaxial growth of perovskite oxides thereon. However,both have merits and demerits. FIG. 1 shows dependency of latticeconstants on temperature on CeO₂ and MgAl₂ O₄ together with dependencyof the lattice constant of Si on temperature.

As shown in FIG. 1, CeO₂ is much more excellent than MgAl₂ O₄ from theviewpoint of lattice match with the single-crystal silicon substrate(when its surface orientation is (100)). However, as to crystallographicstacking alignment when lattice match is established, MgAl₂ O₄ was veryeasy for perovskite oxide (ABO₃) to be stacked thereon, but there was aserious technical bar in front of CeO₂, as shown in FIGS. 2 and 3.

That is, there are many reports stating that CeO₂ (100) does notepitaxially grow even on Si(100), but CeO₂ (110) epitaxially growsthereon. Actually, almost all on CeO₂ among these reports conclude thatnothing but CeO₂ (110)/Si(100) structure is obtained ((21) Appl. Phys.Lett., 59, 3604-3606(1991)). Therefore, in the crystallographic stackingalignment, it is considered difficult to epitaxially grow a perovskiteoxide in (100) orientation thereon.

The Inventor et al., however, succeeded in fabricating a highly orientedfilm of CeO₂ /(100)/Si(100by MOCVD (metal organic chemical vapordeposition). Details of the study were already reported ((18) JapanesePatent Application No. 8-336158, (22) 3rd TIT International Symposium onOxide Electronics (Yokohama, Dec. 18-20, 1996), (23) Japanese PatentApplication No. 8-337241).

Therefore, the Inventor recognized that no substantial technical barstood against realization of CeO₂ (100)/Si(100). As a result, it hasbecome possible to realize crystallographically complete epitaxialgrowth of the perovskite oxide, ABO₃ (100), on CeO₂ as shown in FIG. 4.

Under the background, the CeO₂ (100)/Si(100) structure and itsmanufacturing method proposed by the Inventor in Japanese PatentApplication No. 8-336158 are important. The technique must be useful forintegrating an oxide on a single-crystal silicon substrate.

As to MgAl₂ O₄, since a MgAl₂ O₄ thin film is an excellent base layerfor making a GaAs semiconductor laser, GaN semiconductor laser, ZnOsemiconductor laser, or the like, on a single-crystal silicon substrate,if it is used, all devices to be integrated on single-crystal siliconsubstrates can be made by merely growing thin films without atomic layerbonding, which will be discussed later.

Next discussed are upper electrodes of oxide devices. Platinum (Pt)electrodes are widely known electrodes for ferroelectric materials. (forexample, (24) J. Appl. Phys., 70, 382-388(1991)). A typical example offerroelectric nonvolatile memory devices using Pt electrodes is FeRAMhaving a structure having a PZT thin film sandwiched between a pair ofPt electrodes. However, such FeRAMs were often subjected to peeling-offof Pt electrodes or unacceptable fatigue characteristics showing changeswith time. It is generally acknowledged that several factors, such asshortage of oxygen in the PZT thin film near interfaces with the Ptelectrodes, fatigue of the bonding force caused by large spontaneouspolarization value of PZT, namely, large lattice displacement thereof,and so forth, complexly interact, and cause these problems (for example,(25) J. Appl. Phys., 70, 382-388(1991)).

Since Pt involves a difficulty in processing thereof as well, and alsofrom the viewpoint of preventing oxygen shortage along interfaces, thefollowing oxide electrodes have come to be remarked.

Many were reported on SrRuO₃ electrodes for ferroelectric nonvolatilememory devices, for example, ((26) Science, 258, 1766-1769(1992), (27)Mater. Res. Soc. Symp. Proc., 310, 145-150(1993), (28) Appl. Phys.Lett., 63, 2570-2572(1993), (29) Mater. Res. Soc. Symp. Proc., 341,229-240(1993), (30) E6.8, MRS Fall Meeting at Boston (Nov. 28, 1995),(31) Appl. Phys. Lett., 66, 2197-2199(1995)).

Many were reported also on LaSrCoO₃ here again for ferroelectricnonvolatile memory devices ((32) Appl. Phys. Lett., 63, 3592-3594(1993),(33) Appl. Phys. Lett., 64, 1588-1590(1994), (34) Appl. Phys. Lett., 64,2511-2513(1994), (35) Appl. Phys. Lett., 66, 1337-1339 (1995)).

There are many reports also on superconductive oxide electrodes such asYBCO phase and LSCO phase as electrode here again for ferroelectricnonvolatile memory devices ((36) Science, 252, 944-946(1991), (37) Appl.Phys. Lett., 61, 1537-1539(1992), (38) Appl. Phys. Lett., 63,27-29(1993), (39) Appl. Phys. Lett., 63, 30-32(1993), (40) J. Am. Ceram.Soc., 76, 3141-3143(1993), (41) Appl. Phys. Lett., 64, 1050-1052(1994),(42) Appl. Phys. Lett., 64, 3646-3648(1994), (43) Appl. Phys. Lett., 66,2493-2495(1995), (44) Appl. Phys. Lett., 64, 3181-383(1994), (45) Appl.Phys. Lett., 66, 2069-2071(1995), (46) Appl. Phys. Lett., 67,554-556(1995), (47) J. Appl. Phys., 77, 6466-6471(1995), (48) J. Appl.Phys., 78, 4591-4595(1995), (49) 5th Int. Supercond. Elec. Conf./ISEC'95 (September. 18-21, Nagoya, Japan) (1995) pp.246-248, (50) Jpn. J.Appl. Phys., 33, 5182-5186(1994), (51) Physica C. 235-240,739-740(1994), (52) Appl. Phys. Lett., 66, 299-301(1995), (53) Appl.Phys. Lett., 66, 1172-1174(1995), (54) Appl. Phys. Lett., 67,58-60(1995)).

Especially, it was reported that the use of a conductive oxide having aperovskite-related structure as an electrode material in the same manneras a ferroelectric layer not only would improve the residualpolarization value (for example, (55) Mater. Res. Soc. Symp. Proc., 401,139-149(1996)), but also would restore and improve the fatiguecharacteristics (for example, (56) Jpn. J. Appl. Phys., 33, 5207(1994)).

However, researches and developments made heretofore on ferroelectricnonvolatile memory devices, oxide superconductive devices and oxideoptical devices using LiNbO₃, LiTaO₃, KTa_(1-x) Nb_(x) O₃, or the like(for example, (57) Mater. Res. Soc. Symp. Proc., 341, 253(1994), (58)Mater. Res. Soc. Symp. Proc., 341, 265(1994)) present no substantialconsideration on substrates therefor, and problems remain unsolved.Actually, most of conventional oxide optical devices are single-bodied,and almost none are currently known on those using films grown onsingle-crystal silicon substrates. Considering that almost all are knownon physical properties of ferroelectric bulk single crystals, it will beextremely difficult to find out new physical properties as bulkmaterials. However, under the technical concept of employment ofepitaxial single crystals the present invention intends to realize,although the use of an oxide might enhance it, two dimensionalcompression stress (GPa grade) along the film plane. Therefore, therestill remains the possibility of inducing nonlinear effects that havebeen unknown heretofore, such as optical deflection, optical modulation,higher harmonic waves (second harmonic waves, third harmonic waves,etc.), or ultrasonic physical properties, such as Raman-Nath scattering.

Based on the background, it is a reasonable approach to positively useconductive oxide thin films as electrodes during or at the final stageof a process for stacking oxide thin films on a single-crystal siliconsubstrate (see Literatures (15) through (20)).

As to conductive oxides as electrode materials of oxide devices, thereare many groups of conductive oxides in oxides having perovskite crystalstructures, and they all are candidates of the electrodes. Among theseconductive oxides, examples of simple perovskite oxides expressed thegeneral formula ABO₃ are as follows. ##EQU1##

Among conductive oxides, layered perovskite oxides include: ##EQU2##SrRuO₃, SrIrO₃, Sr₂ RuO₄ Sr₂ IrO₄ are specific examples thereof.

Layered perovskite oxides further include Ba₂ RuO₄, for example.

In addition to these, so-called high-temperature superconductive oxidesare candidates of electrode materials. Some examples thereof are shownbelow.

    (La.sub.1-x Sr.sub.x).sub.2 CuO.sub.4

[x≦0.3]

    (Nd.sub.1-x Ce.sub.x).sub.2 CuO.sub.4-δ

[x≦0.1]

    YBa.sub.2 Cu.sub.3 O.sub.7-δ

    Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+4

[n≦4]

    Tl.sub.m Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+4

[m=1 or 2, n≦5]

As shown above, there are a great deal of candidates of electrodematerials. Among them, Sr--Ru(Ir)--O compounds and superconductiveoxides are particularly interesting because of their non-diffusionproperty. In the former group, SrRuO₃, Sr₂ RuO₄, SrIrO₃ and Sr₂ IrO₄ areexamples of optimum electrode materials because they maintain coherencyof the perovskite crystal structures and are less subject to diffusion.The latter ultrasonic oxides have been reported to be effective indecreasing the size effect when the operation temperature is under thesuperconducting transitional temperature, and are hopeful as futurematerials ((59) Phys. Solid State, 36, 1778-1781(1994)).

Especially, (Nd_(1-x) Ce_(x))₂ CuO_(4-d) which is so-called T' phase, isthe material which was found to become superconductive by solid solutionof Ce into the matrix material of Nd₂ CuO₄ and introduction of oxygendefects by the Inventor et al. (for example, (60) Japanese Patent No.2569780), and it is one of suitable materials for a device processrequiring a high vacuum condition.

Regarding ferroelectric oxide thin film materials to be stacked on anbuffer layer of CeO₂, four conditions must be satisfied, namely, havinga lattice constant close to the lattice constant of CeO₂, having aperovskite-related crystal structure, having a high dielectric constant,having an excellent ferroelectricity, and as more practical requirement,causing no problem of diffusion relative to the underlying buffer layerof CeO₂. Many of perovskite ferroelectric oxides ABO₃ will meet theserequirements, as explained before.

Particularly, realization of the basic crystallographic stackingalignment ABO₃ (001)/CeO₂ (100)/Si(100) on silicon not only enables theuse thereof in some kinds of ferroelectric nonvolatile memory devicesexplained later, but also promises many advantages.

Moreover, from the viewpoint that making good interfaces of ABO₃(001)/CeO₂ (100)/Si(100) is indispensable to reliably prevent trappingwhich is problem from the electrical viewpoint, it will be undoubtedlyeffective for obtaining good interface to make second buffer layers of amaterial having the same perovskite crystal structure and including Cewhich occupies its B site, namely, RceO₃ (R=Ba, Sr, Ca, Pb, Mg, Bi, Li,Ag, Na, K, Y, Ln). This is a material design supported from both theviewpoint of lattice match and the viewpoint of diffusion of elements. Abasic crystallographic stacking alignment on Si, more improved in thissense, is ABO₃ (001)/RCeO₃ (001)/CeO₂ (100)/Si(100). The stackingalignment shown here can be realized by first stacking R atoms on thetop surface of the buffer layer of CeO₂. In this case, it is importantthat the R atom alone is not stacked too much, and it is also importantto promote diffusion of Ce atoms by appropriately controlling thesubstrate temperature or annealing temperature.

As to technologies for making a semiconductor laser or any othersemiconductor light emitting device on a single-crystal siliconsubstrate, there is a method of first cleaning the surface of thesingle-crystal crystal silicon substrate where the device is to be made,and by thereafter epitaxially growing a semiconductor layer directly onthe cleaned area to make the semiconductor light emitting device. Ifdirect epitaxial growth of the semiconductor layer on the single-crystalsilicon substrate is difficult, there is another method of bonding thesemiconductor light emitting device on the single-crystal siliconsubstrate by atomic layer bonding.

Here is explained the technology of atomic layer bonding (also calledcompression bonding). This is a technology that has recently come to beremarked (for example, (61) Kikai Gijutsu Kenkyujo-ho Vol. 50(1996) No.3, 53-55, (62) Nippon Kinzoku Gakkai-shi, Vol. 55 No. 9,1002-1010(1991), (63) Electronic Ceramics Vol. 22 No. 113, 20-26(1991)).The technology can firmly bond two solids without using any bondingagent. Briefly explaining, bonding surfaces of both solids are oncetreated in a high vacuum by ion milling (ion etching) using argon ions,for example, to expose clean surfaces; and both solids are thereafterslowly brought into proper position and close relative contact still ina high vacuum. Due to the close contact, dangling bonds of atoms on theutmost surface of one solid bond to dangling bonds of atoms of theutmost surface of the other solid, and both solids are bound more firmlythan ordinary inter-atom bonding force. Atomic layer bonding needs avapor deposition apparatus and sputtering apparatus, or a high-vacuum orultrahigh-vacuum apparatus such as molecular beam epitaxy (MBE)apparatus, and these apparatuses are required to contain means forpositional alignment and be prepared for simultaneous ion etching. Whenatomic layer bonding is used, a separately prepared semiconductor lightemitting device can be incorporated on a single-crystal siliconsubstrate.

The present invention has been made based on the above-explainedconsideration by the Inventor.

According to the first aspect of the invention, there is provided asilicon-based functional matrix substrate comprising:

a single-crystal silicon substrate having thereon a first region wherethe single-crystal silicon substrate itself appears, and a second regionwhere a cerium oxide layer is preferentially oriented or epitaxiallygrown in the (100) orientation on the single-crystal silicon substrate.

According to the second aspect of the invention, there is provided asilicon-based functional matrix substrate comprising:

a single-crystal silicon substrate having thereon a first region wherethe single-crystal silicon substrate itself appears, and a second regionwhere a magnesium aluminum spinel layer is preferentially oriented orepitaxially grown in the (100) orientation on the single-crystal siliconsubstrate.

According to the third aspect of the invention, there is provided asilicon-based functional matrix substrate comprising:

a cerium oxide layer preferentially oriented or epitaxially grown in(100) orientation on a single-crystal silicon substrate; and

a magnesium aluminum spinel layer epitaxially grown in a selectiveregion on the cerium oxide layer.

According to the fourth aspect of the invention, there is provided asilicon-based functional matrix substrate comprising:

a cerium oxide layer preferentially oriented or epitaxially grown in(100) orientation on a single-crystal silicon substrate; and

a magnesium aluminum spinel layer epitaxially grown on the cerium oxidelayer.

According to the fifth aspect of the invention, there is provided anoptical integrated oxide device comprising:

a single-crystal silicon substrate having thereon a first region wherethe single-crystal silicon substrate itself appears, and a second regionwhere a cerium oxide layer is preferentially oriented or epitaxiallygrown in the (100) orientation on the single-crystal silicon substrate;and

a semiconductor light emitting device formed on the first region byepitaxial growth.

According to the sixth aspect of the invention, there is provided anoptical integrated oxide device comprising:

a single-crystal silicon substrate having thereon a first region wherethe single-crystal silicon substrate itself appears, and a second regionwhere a magnesium aluminum spinel layer is preferentially oriented orepitaxially grown in the (100) orientation on the single-crystal siliconsubstrate; and

a semiconductor light emitting device formed on the first region byepitaxial growth.

According to the seventh aspect of the invention, there is provided anoptical integrated oxide device comprising:

a single-crystal silicon substrate having thereon a first region wherethe single-crystal silicon substrate itself appears, and a second regionwhere a cerium oxide layer is preferentially oriented or epitaxiallygrown in the (100) orientation on the single-crystal silicon substrate;and

a semiconductor light emitting device bonded on the first region byatomic layer bonding.

In the seventh aspect of the invention, typically, at least one of anoptical modulation device and an optical detection device is formed onthe cerium oxide film by epitaxial growth.

According to the eighth aspect of the invention, there is provided anoptical integrated oxide device comprising:

a single-crystal silicon substrate having thereon a first region wherethe single-crystal silicon substrate itself appears, and a second regionwhere a magnesium aluminum spinel layer is preferentially oriented orepitaxially grown in the (100) orientation on the single-crystal siliconsubstrate; and

a semiconductor light emitting device bonded on the first region byatomic layer bonding.

In the eighth aspect of the invention, typically, one of an opticalmodulation device and an optical detection device is formed on themagnesium aluminum oxide film by epitaxial growth.

According to the ninth aspect of the invention, there is provided anoptical integrated oxide device comprising:

a cerium oxide layer preferentially oriented or epitaxially grown in the(100) orientation on a single-crystal substrate, and a magnesiumaluminum spinel layer epitaxially grown in a selective region on thecerium oxide layer; and

a semiconductor light emitting device formed on the magnesium aluminumspinel layer by epitaxial growth, and at least one of an opticalmodulation device and an optical detection device formed on the ceriumoxide layer by epitaxial growth.

According to the tenth aspect of the invention, there is provided anoptical integrated oxide device comprising:

a cerium oxide layer preferentially oriented or epitaxially grown in the(100) orientation on a single-crystal substrate, and a magnesiumaluminum spinel layer epitaxially grown on said cerium oxide layer; and

at least two of a semiconductor light emitting device, an opticalmodulation device and an optical detection device formed on themagnesium aluminum spinel layer formed by epitaxial growth.

In the present invention, the single-crystal silicon substrate is (100)oriented preferably, but (111) orientation is also acceptable in thesecond and sixth inventions.

The optical modulation device and optical detection device typicallyinclude a ferroelectric, piezoelectric or pyroelectric oxide thin film.These ferroelectric, piezoelectric or pyroelectric oxide thin films maybe made of (Ba, Sr, Ca, Pb, Mg, Bi, Ag, Na, K, Y, Sb, Li, Ln)(Ti, Zr,Sn, Th, Ce, Ru, Rh, Ir, Cu, Ga, Al, Nb, Ta, Sb, Bi, Pb)O₃ (whereBa+Sr+Ca+Pb+Mg+Bi+Ag+Na+K+Y+Sb+Li+Ln=1,Ti+Zr+Sn+Th+Ce+Ru+Rh+Ir+Cu+Ga+Al+Nb+Ta+Sb+Bi+Pb=1) having a perovskitecrystal structure, ilmenite crystal structure or GdFeO₃ crystalstructure, or may be made of an oxide artificial superlattice includingtwo or more kinds of oxide thin films.

The semiconductor light emitting device is typically a semiconductorlaser. For example, it may be a GaAs semiconductor laser for redemission, ZnSe semiconductor laser for blue-green emission, GaNsemiconductor laser for blue emission, ZnO semiconductor laser forultraviolet emission ((64) 23rd Int. Conf. on the Physics ofSemiconductors, 2, 1453-1456(1996), (65) 25th Thin Film and SurfacePhysics Seminar (held by Oyc Butsuri Gakkai), Jul. 24-25, 1997, 39-44),for example. Among them, the GaAs semiconductor laser and the ZnSesemiconductor laser had better be bonded by atomic layer bonding becauseepitaxial growth thereof on the single-crystal silicon substrate isdifficult. The GaN semiconductor laser and the ZnO semiconductor laser,however, can be made by epitaxial growth on the single-crystal siliconsubstrate, and need not rely on atomic layer bonding. When the ZnOsemiconductor laser is made by epitaxial growth on the single-crystalsilicon substrate, for example, a (0001)-oriented sapphire (Al₂ O₃) thinfilm may be first epitaxially grown on a (100)-oriented single-crystalSi substrate, and, thereafter, a (0001)-oriented ZnO thin film may beepitaxially grown thereon.

In the case where a ABO₃ layer with a perovskite crystal structure isgrown on a cerium oxide layer on the single-crystal silicon substrate,it is recommended to first grow on the cerium oxide layer a RCeO₃ layer(where R=Ba, Sr, Ca, Mg) having the same perovskite crystal structureand having B site occupied by Ce as a second buffer layer and to growthe ABO₃ layer thereon. This is recommendable from both the viewpoint oflattice match and the viewpoint of diffusion of elements. In this case,the RCeO₃ used as the second buffer layer functions to maintaincrystallographic coherency with the CeO₂ layer as the first buffer layerand to banish electric traps by removing crystalline defects. When aconductive oxide thin film is stacked as an electrode on the ABO₃ layer,since the conductive oxide thin film exhibit good adhesion andcrystallographic coherence to the conductive oxide thin film, it is freefrom peel-off and the problem of fatigue probably caused by a spacecharge layer. This applied not only to oxide devices but also toferroelectric nonvolatile memory devices and superconductive devices.

The invention may interpose an amorphous layer having a thickness notlarger than 20 nm, typically a thickness of several nm to decades nm,between the single-crystal silicon substrate and the overlying ceriumoxide layer or magnesium aluminum spinel layer.

If necessary, the optical integrated oxide device may be bonded to anelectronic refrigerating device, such as compact Peltier device, forcooling purposes.

In the invention having the structure explained above, by using thesilicon-based functional matrix substrate having formed a cerium oxidelayer or a magnesium aluminum spinel layer as a buffer layer on thesingle-crystal silicon substrate, any oxide device, such assemiconductor light emitting device, optical modulation device oroptical detection device, can be integrated thereon by epitaxial growthor atomic layer bonding. In this case, at least oxide devices can beintegrated in a high density because they can be made by firstepitaxially growing an oxide thin film and by thereafter patterning theoxide thin film by lithography. As to semiconductor light emittingdevices, such as GaAs semiconductor lasers or ZnSe compoundsemiconductor lasers, which are difficult to make by epitaxial growth onthe single-crystal silicon substrate, they can be stacked on thesingle-crystal silicon substrate by atomic layer bonding, and anydesired semiconductor light emitting device can be integrated. Moreover,various devices such as semiconductor light emitting device, opticalmodulation device, optical detection device and so on, can be integratedon a common single-crystal silicon substrate. Therefore, the inventionmakes optical signal processing very easy. Furthermore, the devicecharacteristics can be improved remarkably, and a high performance ofthe optical integrated oxide device can be ensured, by using oxide thinfilm superlattice to make oxide thin films as functional thin films ofthe optical modulation device and the optical detection device or byusing materials in which a large two-dimensional compression stressoccurs.

Making oxide devices by epitaxial growth of ferroelectric thin films hasthe meaning of overcoming the size effect. The size effect pertains towhether a ferroelectric thin film maintains the ferroelectricity whendecreased in thickness. This is the phenomenon that a tetragonal crystal(ferroelectric) stable under room temperature suddenly changes to acubic crystal and loses the ferroelectricity when the grain size thereofbecomes smaller than a critical grain size. Conventionally, it wasdiscussed exclusively on particulates. That is, it is a change inphysical property caused by three-dimensional decrease in size. The sizeeffect of a BaTiO , for example, occurs at 0.1 μm. Also for a PZTpolycrystalline thin film, the same effect has been obtained. The sizeeffect can be suppressed significantly by designing the material of theepitaxial growth layer so as to appropriately introduce latticedistortion such as artificial superlattice.

The above, and other, objects, features and advantage of the presentinvention will become readily apparent from the following detaileddescription thereof which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing changes in lattice constant ofMgAl₂ O₄ and CeO₂ with temperature together with changes in latticeconstant of Si with temperature;

FIG. 2 is a schematic diagram showing a crystallographic stackedstructure of ABO₃ /MgAl₂ O₄ /Si(100);

FIG. 3 is a schematic diagram showing a crystallographic stackedstructure of ABO₃ /CeO₄ /Si(100);

FIG. 4 is a schematic diagram showing a crystallographic stackedstructure of ABO₃ /CeO₄ /Si(100);

FIG. 5 is a cross-sectional view of an optical integrated oxide deviceaccording to the first embodiment of the invention;

FIG. 6 is a perspective view for explaining a manufacturing process ofthe optical integrated oxide device according to the first embodiment ofthe invention;

FIG. 7 is a perspective view for explaining a manufacturing process ofthe optical integrated oxide device according to the first embodiment ofthe invention;

FIG. 8 is a perspective view of the optical integrated oxide deviceaccording to the first embodiment of the invention for explaining amanufacturing process thereof;

FIG. 9 is a perspective view of the optical integrated oxide deviceaccording to the first embodiment of the invention for explaining amanufacturing process thereof;

FIG. 10 is a cross-sectional view of the optical integrated oxide deviceaccording to the first embodiment of the invention for explaining amanufacturing process thereof;

FIG. 11 is a cross-sectional view of the optical integrated oxide deviceaccording to the first embodiment of the invention for explaining amanufacturing process thereof;

FIG. 12 is a cross-sectional view of the optical integrated oxide deviceaccording to the first embodiment of the invention for explaining amanufacturing process thereof;

FIG. 13 is a schematic diagram for explaining the concept offerroelectricity induced by lattice distortion;

FIG. 14 is a schematic diagram for explaining the concept offerroelectricity induced by lattice distortion;

FIG. 15 is a perspective view of an optical integrated oxide deviceaccording to the second embodiment of the invention;

FIG. 16 is a perspective view of an optical integrated oxide deviceaccording to the third embodiment of the invention;

FIG. 17 is a perspective view of the optical integrated oxide deviceaccording to the third embodiment of the invention for explaining amanufacturing process thereof;

FIG. 18 is a perspective view of the optical integrated oxide deviceaccording to the third embodiment of the invention for explaining amanufacturing process thereof; for explaining;

FIG. 19 is a perspective view of the optical integrated oxide deviceaccording to the third embodiment of the invention for explaining amanufacturing process thereof;

FIG. 20 is a perspective view of the optical integrated oxide deviceaccording to the third embodiment of the invention for explaining amanufacturing process thereof;

FIG. 21 is a perspective view of the optical integrated oxide deviceaccording to the third embodiment of the invention for explaining amanufacturing process thereof; and

FIG. 22 is a perspective view of the optical integrated oxide deviceaccording to the third embodiment of the invention for explaining amanufacturing process thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention are described below with reference to thedrawings. In all of the drawings showing embodiments of the invention,the same or equivalent elements are shown by common reference numerals.

FIG. 5 is an optical integrated oxide device according to the firstembodiment of the invention.

As shown in FIG. 1, in the optical integrated oxide device according tothe invention, a (100) oriented single-crystal Si substrate 1 has, onits surface, a region A where a cleaned surface of the single-crystal Sisubstrate 1 itself appears, and a region B on which a CeO₂ thin film 2is preferentially (100) oriented or epitaxially grown on the single Sisubstrate 1. The CeO₂ thin film 2 serves as a buffer layer. Thesingle-crystal Si substrate 1 may be either doped or non-doped with animpurity. Actually, a number of these regions A and B are made on thesingle-crystal Si substrate 1, but FIG. 1 shows only one pair forsimplicity.

In the region A where the single-crystal Si substrate 1 itself iscleaned and appears, a GaAs semiconductor laser 3 made by stackingsemiconductor layers on a GaAs substrate to form the laser structureoverlies and is fixed thereon by bonding the bottom surface of the GaAssubstrate thereof by atomic layer bonding. Reference numeral 3a denotesits active layer.

Sequentially stacked on a region of the CeO₂ thin film 2 are a (100)oriented SrRuO₃ thin film 4, (001) oriented PLZT thin film 5 and (100)oriented SrRuO₃ to form an optical modulation device 7. The SrRuO₃ thinfilm 4 and the SrRuO₃ thin film 6 serve as the lower electrode and theupper electrode, respectively. These SrRuO₃ thin films 4 and 6 have aspecific resistance of 100 to 300 μΩ·cm, which is low enough to behaveas electrodes. The PLZT thin film 5 is an optical thin film for opticalmodulation, having nonlinear optical characteristics.

Sequentially stacked on another region of the CeO₂ thin film 2 are a(001) oriented (Nd_(1-x) Ce_(x))₂ CuO₄ thin film 8, (001) orientedPbTiO₃ thin film 9, (001) oriented (Nd_(1-x) Ce_(x))₂ CuO₄ thin film 10,(100) oriented CeO₂ thin film 11, (001) oriented (Nd_(1-x) Ce_(x))₂ CuO₄thin film 12, (001) oriented PbTiO₃ thin film 13 and (001) oriented(Nd_(1-x) Ce_(x))₂ CuO₄ thin film 14. The (Nd_(1-x) Ce_(x))₂ CuO₄(Nd_(1-x) Ce_(x))₂ CuO₄ thin film 8, PbTiO₃ thin film 9 and (Nd_(1-x)Ce_(x))₂ CuO₄ thin film 10 form a pyroelectric device behaving as anoptical detection device 15. The (Nd_(1-x) Ce_(x))₂ CuO₄ thin film 12,PbTiO₃ thin film 13 and (Nd_(1-x) Ce_(x))₂ CuO₄ 14 form anotherpyroelectric device as another optical detection device 16. The(Nd_(1-x) Ce_(x))₂ CuO₄ thin film 8 and (Nd_(1-x) Ce_(x))₂ CuO₄ thinfilm 10 are used as the lower electrode and the upper electrode of theoptical detection device 15, whereas the PbTiO₃ thin film 9 forms apyroelectric thin film thereof. Similarly, the (Nd_(1-x) Ce_(x))₂ CuO₄thin film 12 and (Nd_(1-x) Ce_(x))₂ CuO₄ thin film 14 are used as thelower electrode and the upper electrode of the optical detection device16, whereas the PbTiO₃ thin film 13 forms a pyroelectric thin filmthereof. The CeO₂ thin film 11 is an insulating layer for electricallyinsulating the optical detection devices 15 and 16 from each other.

In the optical integrated oxide device having the above-explainedstructure according to the first embodiment, light L emitted from theactive layer 3a of the semiconductor laser 3 enters into the opticalmodulation device 7. Then, a voltage is applied across the SrRuO₃ thinfilm 4 as the lower electrode of the optical modulation device 7 and theSrRuO₃ thin film 6 as the upper electrode thereof to change therefractive index of the PLZT thin film 5 normal to the propagatingdirection of L. Thus the light L is diffracted. The diffraction angle oflight L depends upon the length of the optical path for light passingthrough the optical modulation device 7 and its electrooptical constant.Therefore, by utilizing two-dimensional distortion in the PLZT thin film5, which will be explained later, a large diffraction angle neverattained heretofore can be obtained, and enables reliable signalprocessing.

Next explained is a manufacturing process of the optical integratedoxide device according to the first embodiment.

First, a single-crystal Si substrate 1 as shown in FIG. 6 is prepared.Any size of the single-crystal Si substrate 1 is selected appropriately,but one with a large diameter as large as 8 inches may be used.

Next as shown in FIG. 7, after the surface of the single-crystal Sisubstrate 1 is cleaned by RCA cleaning, the cleaned surface is coveredwith a mask 17. Any material is selected as the mask 17, such as Au.

Next as shown in FIG. 8, part of the surface of the single-crystal Sisubstrate 1 not covered by the mask 17 is hydrogen terminated.

Next as shown in FIG. 9, the CeO₂ thin film 2 is epitaxially grown inthe (100) orientation on the hydrogen-terminated part of thesingle-crystal Si substrate 1 not covered by the mask 17 by MOCVD. Theepitaxial growth of the CeO₂ film 2 by MOCVD is performed in thefollowing manner. Using a hot wall type reaction vessel, a metal organiccompound material, Ce(DPM)₄ (often abbreviated to Ce(thd)₄. DPM pertainsto di-pivaloyl methane, and thd is 2, 2, 6, 6-tetramethyl-3,5-heptanedion) is used as the Ce source material. Used as the carriergas is a mixed gas of argon (Ar) and oxygen (O₂). The reaction vessel istypically evacuated to 10 Torr or lower. During the epitaxial growth ofthe CeO₂ thin film 2 by MOCVD, if the substrate temperature exceeds 700°C., the CeO₂ thin film 2 epitaxially grown thereon gradually changes insurface orientation from (100) to (111). Therefore, the substratetemperature during growth is preferably set not to become higher than700° C. On the other hand, if the substrate temperature goes down under600° C., the CeO₂ thin film grown thereon seriously degrades incrystalline quality. Therefore, the optimum range of the substratetemperature is 600 to 700° C. The CeO₂ thin film 2 grown in this mannerhas a thickness in the range of 30 to 100 nm.

Next, as shown in FIG. 10, the (001) oriented (Nd_(1-x) Ce_(x))₂ CuO₄thin film 8 is epitaxially grown on the CeO₂ thin film 2 by MBE, forexample. Here, the substrate temperature is set within 600 to 800° C.,for example. If it is thereafter post-annealed at a temperature of 800°C., for example, the (Nd_(1-x) Ce_(x))₂ CuO₄ gets a higher electricconductivity due to self-diffusion of Ce from the CeO₂ thin film 2.

Next grown epitaxially is the (001) oriented PbTiO₃ thin film 9 by MBE.The epitaxial growth of the PbTiO₃ thin film 9 by MBE may be done asfollows, for example. In an ultra-high vacuum container of an MBEapparatus, a vaporizing source of Ti using electron beams and avaporizing source of Pb using Knudsen cell (K cell) are prepared. Then,while introducing well-controlled O₂ gas into the ultra-high vacuumcontainer, maintaining the total pressure to approximately 10⁻⁴ Torr,appropriately controlling the Ti vaporizing rate by electron beams andthe shutter of the K cell of Pb, detecting reflection high energyelectron diffraction (RHEED) oscillations, and using them for feedbackcontrol, the growth is progressed. During the growth, the substratetemperature should be set within 500 to 900° C., for example. Morepreferably, the temperature is 700° C. or higher to ensure a betterquality film.

After that, in the same manner as already explained, epitaxially stackedsequentially are the (001) oriented (Nd_(1-x) Ce_(x))₂ CuO₄ thin film10, (100) oriented CeO₂ thin film 11, (001) oriented (Nd_(1-x) Ce_(x))₂CuO₄ thin film 12, (001) oriented PbTiO₃ thin film 13 and (001) oriented(Nd_(1-x) Ce_(x))₂ CuO₄ thin film 14.

Thereafter, a mask (not shown) made of SiO₂ is formed on the (Nd_(1-x)Ce_(x))₂ CuO₄ thin film 14. Then, using the mask, the (Nd_(1-x) Ce_(x))₂CuO₄ thin film 14, PbTiO₃ thin film 13, (Nd_(1-x) Ce_(x))₂ CuO₄ thinfilm 12, CeO₂ thin film 11, (Nd_(1-x) Ce_(x))₂ CuO₄ thin film 10, PbTiO₃thin film 9 and (Nd_(1-x) Ce_(x))₂ CuO₄ thin film 8 are patterned byetching. As a result, the optical detection devices 15 and 16 areobtained as shown in FIG. 10.

Next, while covering surfaces of the optical detection devices 15 and 16with a mask (not shown) made of SiO₂, for example, the (100) orientedSrRuO₃ thin film 4 is grown epitaxially by MBE, for example. The SrRuO₃thin film 4 is originally orthorhombic. During epitaxial growth,however, its crystal structure changes from a quasi perovskite structureto a perovskite structure.

Similarly, the PLZT thin film 4 and the SrRuO₃ thin film 5 are nextepitaxially grown sequentially by MBE.

Then, the mask 17 is removed to expose the surface of the single-crystalSi substrate 1 heretofore covered.

Next, as shown in FIG. 12, the exposed surface of the single-crystal Sisubstrate 1 is cleaned by argon ion etching. On the other hand, the GaAssemiconductor laser 3 is prepared separately by epitaxially growing GaAssemiconductor layers on a GaAs substrate and by making the upperelectrode. In the same ultra-high vacuum chamber, the bottom surface ofthe GaAs substrate of the GaAs semiconductor laser 3 is cleaned by argonion etching. After that, in the same ultra-high vacuum chamber, the GaAssemiconductor laser 3 is properly positioned on the exposed surface ofthe single-crystal Si substrate 1, and the bottom surface of the GaAssubstrate is brought into close contact with the surface of the surfaceof the single-crystal Si substrate 1. As a result, the surface of thesingle-crystal Si substrate 1 and the bottom surface of the GaAssubstrate of the GaAs semiconductor laser 3 are bonded by atomic layerbonding.

After that, the single-crystal Si substrate 1 is divided into chips. Asa result, the intended optical integrated oxide device shown in FIG. 5is completed.

According to the first embodiment, the following various advantages areobtained. That is, basic optical devices, namely, GaAs semiconductorlaser 3, optical modulation device 7 and optical detection devices 15and 16, can be integrated in a high density on the single-crystal Sisubstrate 1. Additionally, since the GaAs semiconductor laser 3 ispreviously fabricated separately in an ordinary manufacturing processand bonded to the single-crystal Si substrate 1 by atomic layer bonding,its integration is easier than epitaxially growing semiconductor layersdirectly on the single-crystal Si substrate 1. Moreover, since the oxidethin films forming the optical modulation device 7 and the opticaldetection devices 15 and 16 are made by epitaxial growth, quite a largetwo-dimensional compression stress as large as several GPa degrees,which has never expected heretofore, can be produced in their functionalthin film portions, namely, the PLZT thin film 5 of the opticalmodulation device 7 and the PbTiO₃ thin films 9 and 13 of the opticaldetection devices 15 and 16, and the nonlinear optical characteristicscan be improved remarkably. In this respect, images on the concept offerroelectricity induced by lattice distortion are shown in FIGS. 13 and14, because there can be expected a surprising ferroelectricityresulting from a keen increase in Curie point caused by two dimensionalcompression stress introduced by lattice mismatching with the baselattice. Since this physical property depends on the thickness from thebase layer, a superlattice period within an extent out of latticerelaxation will be appropriate.

As explained above, according to the first embodiment, the opticalintegrated oxide device with excellent characteristics, highreliability, high integration and high density can be realized byoptimization of the structure.

FIG. 15 shows an optical integrated oxide device according to the secondembodiment of the invention. As shown in FIG. 15, in the opticalintegrated oxide device according to the second embodiment, the opticalmodulation device 7 is made of a PLZT thin film having formed thereoncomb-shaped electrodes 18a, 18b. In the optical modulation device 7, adistribution of refractive index can be made along the plane of the PLZTthin film 5 by applying a voltage across the comb-shaped electrodes 18a,18b. Therefore, light entering into the optical modulation device 7 canbe changed in propagating direction within the plane. In this respect,the optical detection devices 15 and 16 are aligned in a transversedirection (parallel to the substrate surface). In the other respects,the embodiment shown here is the same as the optical integrated oxidedevice according to the first embodiment, and explanation thereof isomitted here.

According to the optical integrated oxide device according to the secondembodiment, in addition to the same advantages as those of the opticalintegrated oxide device according to the first embodiment, there is anadditional advantage that it enables signal processing by transversetransmission of the optical signal.

FIG. 16 shows an optical integrated oxide device according to the thirdembodiment of the invention. As shown in FIG. 16, in the opticalintegrated oxide device according to the third embodiment, a MgAl₂ O₄thin film 22 in (111) orientation is epitaxially grown on a (111)oriented single-crystal Si substrate 21. The MgAl₂ O₄ thin film 22 is abuffer layer.

In a given location on the MgAl₂ O₄ thin film 22, a GaN semiconductorlayer 23 is made by epitaxial growth.

On another location of the MgAl₂ O₄ thin film 22, a SrRuO₃ thin film 24is stacked, and a LiNbO₃ thin film 25 is stacked on the SrRuO₃ thin film24. In an upper portion of the LiNbO₃ thin film 25, a periodic domaininverted layer 26 is built in. The SrRuO₃ thin film 24, LiNbO₃ thin filmand periodic domain inverted layer 26 form a second harmonic generatingdevice 27. The SrRuO₃ thin film 24 is its electrode.

In the optical integrated oxide device having the above-explainedstructure according to the third embodiment, laser light of thefrequency ω generated from the GaN semiconductor laser 23 passes throughthe second harmonic generating device 27, and light of the frequency 2ω, e.g. second harmonic wave, is obtained.

Next explained is a manufacturing process of the optical integratedoxide device according to the third embodiment.

First, as shown in FIG. 17, after the surface of the (111) orientedsingle-crystal Si substrate 21 is cleaned by RCA cleaning, the cleanedsurface is hydrogen terminated.

Next, as shown in FIG. 18, the MgAl₂ O₄ thin film 22 is epitaxiallygrown on the single-crystal Si substrate 21 by MOCVD. The epitaxialgrowth of the MgAl₂ O₄ thin film 22 by MOCVD is performed in thefollowing manner. As a metal organic compound, here is used a complexmetal alkoxide, magnesium di-aluminum isopropoxide (MgAl₂ (OC₃ H₇)₈).The complex metal alkoxide significantly facilitates growth of astoichiometric composition, using a single source of source materials.It is not easy to independently control a metal organic compound sourcematerial of Mg and a metal organic compound source material of Al.However, when the complex metal alkoxide is used as the source material,it is sufficient to control a single vapor pressure before thetemperature exceeds its decomposition temperature, and growth can bemade very easily. More specifically, by keeping a single body of MgAl₂(OC₃ H₇)₈ at a predetermined temperature, thereby maintaining a constantvapor pressure and using a source material gas produced thereby, thegrowth is effected. An appropriate temperature of the substrate duringthe growth is, for example 700° C.

There is a proposal to once solve the complex metal alkoxide MgAl₂ (OC₃H₇)₈ into an organic solvent and introducing it into an atomizer toobtain the source material gas ((66) J. Mater. Res., 9,1333-1336(1994)). This method might be excellent in growth rate;however, it is not certain whether a good quality film can be made. Thereport certainly reports on epitaxial growth of a MgAl₂ O₄ thin film onSi(100) and Mg(100), but films obtained thereby are all thick. Itappears that thick grown films merely result in maintaining an epitaxialrelationship with the base layers, and epitaxial property of the thinfilm itself cannot be estimated only from this.

Next as shown in FIG. 19, a mask 27 is formed on a predetermined regionof the MgAl₂ O₄ thin film 22.

Then, as shown in FIG. 20, on a region of the MgAl₂ O₄ thin film 22 notcovered by the mask 27, the GaN thin film 28 in (0001) orientation isepitaxially grown by MOCVD. For the epitaxial growth of the GaN thinfilm 28, trimethyl gallium (TMGa) and ammonia (NH₃), for example, areused as the source material. It was already reported that a (0001)oriented GaN thin film epitaxially grew on a (111) oriented MgAl₂ O₄thin film ((67) Appl. Phys. Lett., 68, 337-339(1996), (68) Appl. Phys.Lett., 68, 1129-1131(1996)).

Next, on the GaN thin film 28, GaN semiconductor layers including aGaN/InGaN heterojunction are epitaxially grown sequentially by MOCVD,and are patterned into a predetermined configuration by etching. As aresult, the GaN semiconductor laser 23 is made as shown in FIG. 21. Themethod for making a GaN semiconductor laser was already reported (forexample, (69) Appl. Phys. Lett., 62, 2390(1993)).

Next, as shown in FIG. 22, the (111) oriented SrRuO₃ thin film 23 isepitaxially grown on another predetermined region of the MgAl₂ O₄ thinfilm 22 by MOCVD or MBE.

Further grown epitaxially is the LiNbO₃ thin film 25 by MBE or MOCVD.

Then, after a Pt film is formed on the LiNbO₃ thin film 25 by vapordeposition, for example, the Pt film is patterned by etching to form apoling comb-shaped electrode 29.

After that, a predetermined pulsating voltage is applied across theSrRuO₃ thin film 23 as the lower electrode and the poling comb-shapedelectrode 29, to make a periodic polarization inverted structure,namely, periodic domain inverted layer 26, in the upper portion of theLiNbO₃ thin film 25. The poling method are reported in detail ((70)Appl. Phys. Lett., 62, 435-436(1993)).

The poling comb-shaped electrode 29 is next removed by etching.

Having described specific preferred embodiments of the present inventionwith reference to the accompanying drawings, it is to be understood thatthe invention is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein by one skilledin the art without departing from the scope or the spirit of theinvention as defined in the appended claims.

For example, in the first and second embodiments, a thin film of anartificial superlattice, (SrTiO₃)_(n) (PbTiO₃)_(m), for example, may beused in lieu of the PbTiO₃ thin films 9, 13 of the optical detectiondevices 15, 16. In this case, it would be needless to say that theperovskite PbTiO₃ (001) film epitaxially grows with a more sufficientlattice distortion than the lattice constant in bulk.

In the first embodiment, a (SrCa)RuO₃ thin film, Sr₂ RuO₄ thin film,superconductive oxide thin film, and so on, may be used instead of theSrRuO₃ thin films 4 and 6 forming electrodes of the optical modulationdevice 7. When a Sr₂ RuO₄ thin film is used, its orientation should be(001).

In the second embodiment, a superlattice of a LiNbO₃ thin film and aLiTaO₃ thin film may be used in lieu of the LiNbO₃ thin film 26 of thesecond harmonic generating device 28. By using the LiNbO₃ /LiTaO₃superlattice, a higher efficiency is expected. MBE is an appropriatemethod for growth of the LiNbO₃ /LiTaO₃ superlattice. The crystalstructure obtained thereby is not an ilmenite crystal structure, but aperovskite-regulated crystal structure as far as films are not thick.Therefore, their orientation will be (111). In this case, however, sincethese films are poled by the poling comb-shaped electrodes 29, they neednot be oriented so. Furthermore, a K(Nb_(1-x) Ta_(x))O₃ thin film, forexample, may be used instead of the LiNbO₃ thin film 26. The polingcomb-shaped electrode 29 may be left there without removing it, ifappropriate. This is because second harmonic waves with the halfwavelength can be obtained when light enters into the periodic domaininverted layer 27.

In the first, second and third embodiments, the use of MOCVD or MBE areproposed as methods for growing thin films. However, any otherappropriate atomic layer growth method, such as reactive evaporation orlaser abrasion (often called pulse laser deposition or laser MBE), maybe employed.

As explained above, according to the silicon-based functional matrixsubstrate according to the invention, both an oxide device such as oxideoptical device, ferroelectric nonvolatile memory, oxide superconductivedevice, and so forth, and a semiconductor light emitting device such assemiconductor laser can be integrated in an optimum structure on acommon substrate.

According to the optical integrated oxide structure according to theinvention, both an oxide device such as oxide optical device,ferroelectric nonvolatile memory, oxide superconductive device, and soforth, and a semiconductor light emitting device such as semiconductorlaser can be integrated in an optimum structure on a common substrate.

What is claimed is:
 1. A silicon-based functional matrix substratecomprising:a single-crystal silicon substrate having thereon a firstregion where said single-crystal silicon substrate itself appears; afirst buffer layer of cerium oxide is preferentially oriented orepitaxially grown in the (100) orientation on a second region of saidsingle-crystal silicon substrate; and a second buffer layer on theopposite surface side of said cerium oxide layer to said single-crystalsilicon substrate, said second buffer layer being a material having aperovskite crystal structure and including Ce which occupies its B site.2. The silicon-based functional matrix substrate according to claim 1wherein said single-crystal silicon substrate is (100) oriented.
 3. Asilicon-based functional matrix substrate comprising:a cerium oxidelayer preferentially oriented or epitaxially grown in (100) orientationon a (100) oriented single-crystal silicon substrate; and a magnesiumaluminum spinel layer epitaxially grown in a selective region on saidcerium oxide layer.
 4. A silicon-based functional matrix substratecomprising:a cerium oxide layer preferentially oriented or epitaxiallygrown in (100) orientation on a (100) oriented single-crystal siliconsubstrate; and a magnesium aluminum spinel layer epitaxially grown onsaid cerium oxide layer.
 5. The silicon-based functional matrixsubstrate according to claim 1, wherein said second buffer layer is amaterial having a perovskite crystal structure of RCeO2, which R isselected from the group consisting of Ba, Sr, Ca, Pb, Mg, Bi, Li, Ag,Na, K, Y and Ln.